For my long trip, I've just used a "self-storage" company. A quick search reveals that these exist in Ireland too (e.g. http://www.spacestorage.ie/ ). Not sure about Ireland but I know that in the US / Canada, if you pay more you can get a climate-controlled, secure facility (the security aspect is really important, storage break-ins are a common occurrence). For the really expensive electronics and items with especially great sentimental value, I would just leave them with friends.
You can even find fancy self-storage features, e.g. the place I used could receive packages (so I could, for example, send unneeded stuff back home during my trip, and the company would put it into the storage unit).
If you're worried about dampness, besides getting a climate-controlled storage unit, try getting a unit that's above the ground floor (also better for security), and buy some big packs of silica gel and put it in sealed plastic bags with your stuff, and pack these bags into boxes.